Eberspacher with two controllers

Sometimes users would like to add a second controller for operating their Eberspacher heater.

Typical uses are one controller in the main area with an additional controller near the bed or for switching between two controllers with different temperature settings for day or night use.

I had one in the cab and another in the back of my van, just extend an arm from under the covers, luxury on a cold morning!

It would be ideal to have both controllers active all the time with the Eberspacher responding automatically to changes made to either controller. However that would require fairly sophisticated circuitry beyond the capability of most of our users. I may try developing such a system later.

For the present we have to switch manually between the two controllers.

I used a 4 pole 2 position switch. Also known as a 4p2w switch On - On.

801, 701, Mini or Rheostat controllers can be used as Controller 1 or 2 and in any combination.

If you are unsure I can produce the circuit for any combination, email me.

Some older controllers can also be used providing they are compatible with the heater, identify their wiring and connect to the switch like a Rheostat.

Personally I prefer to avoid any of the EasyStart controllers. Additionally they use a different control method and are not shown here.

The above drawings are how I switch controllers for modern heaters like Airtronic D2, D1LCC and D1LC.

Users with some electrical knowledge may want to change the wiring to suit their own need.

Some users will leave the red wire unswitched. The reason I personally switch the red (+12V) wire is I want the unused controller to be completely dead, otherwise you can end up adjusting the wrong one and not realise it is non operational.

Similarly to make the switching simpler some users will make the yellow unswitched, just connecting the two in parallel. That will probably work ok but it depends upon the controller circuit design. Both controllers have to be off for the heater to switch off.

The grey/red must be switched, only the selected controller can set the target temperature.

Similarly only one controller can be connected to the blue/white diagnostics wire and only one external temperature sensor can be connected to the grey.

The spare switch element *User spare can be wired to switch the blue/white or grey if needed, or it could switch power to a LED to indicate which controller is in use.

Perfectionists may comment that I have not used British Standard drawing symbols.

I know, I have been a professional engineer (AMIEE) for longer than I care to remember. I use non standard symbols because I am not instructing engineers or technicians, our site is aimed at the general public and they understand the drawings better when drawn this way.

Practical points

The appropriate controller has to be selected manually.

There is a very short break in the signals to the Eberspacher while the switch contacts changeover. That might cause the heater to shut down and then restart.

I had a switch fail which needed to be replaced. Fortunately I had thought of this possibility and connected the switch wiring to the Eberspacher and the controllers using spade terminals, male spades on wires towards heater, female spades towards controllers. That meant I could disconnect the switch and connect one controller to the heater until I could replace it.